The present invention relates to a rotational speed adjusting device for a pneumatic rotational tool for controlling the maximum rotational frequency of the pneumatic rotational tool so as not to exceed some extent.
A pneumatic rotational tool such as an air grinder, an air sander and so on is a tool in which a rotational grinding article such as a grindstone or a processing tool such as a rotational polishing article to polish an article to be polished. The processing tool is good in grinding property and polishing property and excellent in workability when the tool is operated at high speed as compared with low speed.
In the pneumatic rotational tool, in general, using pressure (normal pressure) is indicated in an instruction manual or the like. However, the actual circumstances are that the indication of the using pressure is ignored, and the tool is used at far high pressure. As shown in FIG. 7, if air pressure is raised, rotational frequency of the processing tool exceeds allowable rotational frequency as shown by phantom lines (a).
When the pneumatic rotational tool exceeds in allowable rotational frequency, a turning effort (a centrifugal force) in excess of strength exerts on the processing tool to possibly break the processing tool. When the processing tool is broken, the broken matter scatters in all directions so that an operator and persons round are possibly injured, which is very dangerous. From a viewpoint of this, it was necessary for the pneumatic rotational tool such as n air grinder, an air sander and so on to suppress rotational frequency to a level less than the maximum allowable rotational frequency. That is, preferably, the rotational frequency does not exceed allowable rotational frequency as in the solid line (b) in FIG. 7.
Further, for maintaining the pneumatic rotational tool so as not to exceed the allowable rotational frequency, quantity of supplied air is automatically controlled so that rotational frequency of a motor repeats to be increased and decreased within the range of predetermined rotational frequency. There was a disadvantage in that in the repeating operation of increase or decrease of the rotational frequency of a motor, axial expansible vibrations occur in a speed adjusting member of a rotational speed adjusting device.